Coverage analysis tool for optical data

Module using the sepal_ui framework and an interactive Voila dashboard to create maps of cloud-free observations for major optical satellites as available on Google’s Earth Engine Platform.

The framework follows the logic of bfasts’ countObs and summaryBrick functions as described here.

For bfast specific requirements check Schultz et al. 2013 for further background.

The process is done in 3 steps described in the below sections:

Select an AOI

Using the provided AOI selector, select an AOI of your choice between the different methods available in the tool. We provide 3 administration descriptions (from level 0 to 2) and 3 custom shapes (drawn directly on the map, asset or shapefile).

aoi selector

Note

If a custom aoi from shape or drawing is selected, you will be able to use it directly and the upload to GEE will be launched in the background

Select dataset parameters

To perform the bfast preanalysis you need to provide the tool with key parameters:

• date range: The start and end date of your analysis

• sensors: The list of sensors you want to use (Landsat missions & Sentinel-2)

• Tier 2: Tier 2 images of the Landsat missions (this might lead to wrong results)

• SR: whether to use Surface Reflectance images (SR). default to Top of atmosphere (TOA)

Once all your parameters are selected you need to click on the button to make your selection effective

Display dataset

After having selected your parameters you can move to the Visualization tile. Select one of the statistical measures to display in the following list:

• Cloud-free pixel count

• Total pixel count (i.e. scene coverage)

• NDVI Median

• NDVI Std. Dev.

You can also decide to produce stats on yearly basis using the provided switch

Note

The image will be dynamically re-evaluated and re-centered on every change

Export dataset

Once you’re happy with the information displayed then can be exported to be further used in a GIS software or in a GEE process. The tool provides 2 main exportation options, as an asset(in GEE) or as a Tif file in SEPAL.

Both use the GEE export system and share the same set of parameter:

• statistical measures to export

  • count of cloud-free observation per pixel

  • NDVI’s median of cloud-free observations

  • NDVI's std. dev. of cloud-free observations

  • count for all observations per pixel

• time-period

  • full timespan calculation(s)

  • annual calculation(s)

• scale: the resolution (in meters) to us in GEE exported file

Danger

When the image is exported to SEPAL, you cannot quit the application until the downloading is finished.